Such a micromechanical sensor unit is discussed in the patent publication DE 10 2006 016 260 A1, for example, and allows multiple different sensor elements having different requirements in regard to the atmosphere surrounding them to be combined in one micromechanical sensor unit. The different sensor elements, typically an acceleration sensor and a rotation rate sensor, are situated in different cavities for this purpose and may include a seismic mass. For such micromechanical devices, it is generally provided to manufacture the different sensor elements simultaneously, i.e., in one method step, on a substrate, whereby particularly small and cost-effective combinations of different sensor systems are implementable in a single micromechanical sensor unit. The technical challenge for the micromechanical sensor units in question is to operate the sensor elements at the pressure which is intended for them in each case, which differs in most cases. While namely a low pressure (approximately 1 mbar) may be desirable for a rotation rate sensor, for example, so that the resonantly driven seismic mass of the rotation rate sensor experiences only minor damping, acceleration sensors may be operated at a pressure which is approximately 500 times greater. The related art usually uses getter materials for setting the desired pressure which differs from cavity to cavity. For example, this getter material is introduced into the cavity for which a low pressure is provided, and in an activated state is able to trap gas molecules, whereby the gas pressure in the cavity decreases. The getter material is usually activated by the temperature exceeding a threshold value. The use of additional getter materials, which are consequently associated with additional costs, in the manufacture of the micromechanical sensor unit proves to be a disadvantage in this case. It is the object of the present invention to make a micromechanical sensor unit available in which, on the one hand, sensor elements in different cavities having different pressures are combined; on the other hand, it may be implemented cost-effectively and without great complexity.